The present invention relates to a handover method for a CDMA mobile communication using a spread spectrum signal, for a base station and a mobile station of the same.
The CDMA method is a leading candidate for the next generation of mobile communication systems as a multiple access method capable of rapidly increasing the system capacity (number of channels). Progress is being made in standardization for practical use.
Presently, in the wideband CDMA mobile communication system being standardized, communication information between a base station and a mobile station is spread in frame units. The frame units are obtained by partitioning the information into predetermined lengths, for example, 10 msec (hereinafter, this frame unit will be referred to as a xe2x80x9cradio framexe2x80x9d).
An upstream traffic channel signal from a mobile station is spread using a spreading code initialized for every xe2x80x9csuper framexe2x80x9d comprised of 72 radio frames as a unit period. For this reason, when performing control to switch (handover) a communication channel from a first base station in communication to a second base station when a mobile station moves from a radio zone of the first base station to a radio zone of the second base station, it is necessary to synchronize the upstream traffic channel signal in communication with the phase of the spreading code at the second base station for reception of the upstream traffic channel.
In other words, it is necessary to correct the discrepancy of frame numbers (corresponding to the phases of the spreading code) of the radio frame between the first base station in communication and the second base station. Further, it is necessary to correct the discrepancy of frame timings within one frame time. For this reason, a perch channel signal giving reference timing for measuring the discrepancy of the timings of the radio frames is transmitted from the second base station. The mobile station measures the discrepancy of the radio frames between the first base station in communication and the second base station based on this perch channel signal, and then sends the information to the first base station in communication. The second base station receives the information via a higher rank communication network and corrects the radio frame number for receiving the upstream traffic channel signal and the timing thereof, that is, the phase of the radio frame, according to the information.
FIG. 16 shows the phase correction of the radio frame of the related art. (A) of the figure shows a transmission radio frame for a downstream traffic channel signal of a first base station BS1 in communication. (B) of the figure shows a received radio frame of the downstream traffic channel signal of a mobile station MS before handover. (C) of the figure shows a transmission radio frame of the upstream traffic channel signal of the mobile station MS.
(D) of the figure shows the transmission radio frame of the perch channel signal of a second base station BS2. (E) of the figure shows the reception radio frame of the perch channel signal of the mobile station MS and (F) of the figure shows the reception radio frame of the upstream traffic channel signal of the second base station BS2.
Further, (G) of the figure shows the transmission radio frame of the downstream traffic channel signal of the second base station BS2. (H) of the figure shows the receiving frame of the downstream traffic channel signal of the mobile station MS after handover.
The transmission radio frame (A) of the downstream traffic channel signal from the first base station BS1 is received at the mobile station MS along with a propagation delay of the radio section. The mobile station transmits the radio frame (C) in the upstream traffic channel after an elapse of a predetermined timing (1024 chips) from the reception radio frame (B) of the downstream traffic channel signal.
At the time of the handover, the mobile station MS receives (E) the perch channel signal transmitted (D) from the second base station BS2. The mobile station then extracts the frame number written in each radio frame of the perch channel and, measures the discrepancy between that frame number and the frame number of the upstream traffic channel presently being transmitted, and the discrepancy of the timings of the radio frames within one frame. The mobile station MS sends radio frame phase discrepancy information TDHO indicating the discrepancy of these frame numbers and the discrepancy of the timings of the radio frames within one frame to the first base station.
The first base station BS1 sends the radio frame phase discrepancy information TDHO to the second base station BS2 via the higher rank communication network. The second base station BS2 then corrects the reception phase of the radio frame in the upstream traffic channel based on the radio frame phase discrepancy information TDHO and brings the phase of the reception radio frame (F) of the upstream traffic channel signal of the second base station BS2 into coincidence with the phase of the transmission radio frame (C) of the upstream traffic channel signal from the mobile station MS. Note that the phase correction of the propagation delay in the radio section is also carried out.
The second base station BS2 transmits (G) the downstream traffic channel signal with a timing advanced from the phase of the reception radio frame (F) of the upstream traffic channel signal by 1024 chips. The reason for this is that, as mentioned above, the mobile station transmits the radio frame in the upstream traffic channel after the timing of 1024 chips from the phase of the reception radio frame (H) of the downstream traffic channel signal, so as to coincide with that timing.
In other words, in the phase correction of a radio frame of the related art, the mobile station MS must extract the frame number written in the radio frame in the perch channel and measure the discrepancy of the timings of the radio frames within one frame between the perch channel and the upstream traffic channel.
In view of the above discussion, when frequency bands used between the base stations differ, it is necessary that a mobile station receive a downstream traffic channel signal from the base station in communication at the time of handover. It is also necessary that the mobile station receives a perch channel signal transmitted by the second base station while despreading and decoding the downstream traffic channel. Further, the perch channel must also be despread and decoded to extract the frame number thereof Thus, the functional circuits of a mobile station have become complex. However, since a mobile station should have a minimal size and weight, it would be highly desirable to reduce the complexity of the functional circuits.
An object of the present invention is to realize handover which corrects the discrepancy of the frame numbers on the base station side and establishes a synchronization after handover to thereby make extraction of the frame number in the perch channel in the mobile station unnecessary.
Another object of the present invention is to reduce the processing load of the mobile station, and optimally correct the phase of the radio frame.
These and other objects are met by a handover method in CDMA mobile communication according to the present invention that includes a handover method in CDMA mobile communication for transmitting and receiving between a mobile station and a base station in both an upstream traffic channel signal and a downstream traffic channel signal. This communication is performed in units of a radio frame having a predetermined length, for spreading the upstream traffic channel signal from the mobile station to the base station by a spreading code having a plurality of periods in the radio frames as one period and transmitting the spread signal.
The handover method includes a step of, at the mobile station, measuring a time difference of frame timings within one frame between the radio frame of a traffic channel with a first base station in communication and the radio frame of a perch channel from a second base station of a destination of the handover. Further sending the time difference information of frame timing within the one frame to the first base station. A step of, at the first base station sending a time difference information of the frame timing within one frame and the frame number of the radio frame which is sent from the mobile station of the traffic channel in communication, via a higher rank communication network to the second base station.
A step of at the second base station, performing a phase correction for bringing the phase of the spreading code for receiving the radio frame in the upstream traffic channel of the second base station into coincidence with the phase of the spreading code in the upstream traffic channel from the mobile station. This is accomplished using the time difference information of the frame timing within one frame and the frame number of the radio frame of the traffic channel in communication, which are both sent from the first base station.
The handover method according to the present invention includes additional steps of, at the second base station when synchronization cannot be established even if despreading the radio frame signal in the upstream traffic channel transmitted from the mobile station by a spreading code of a phase corresponding to the frame number of the radio frame in the traffic channel in communication; which is sent by the first base station.
The method includes advancing the phase of the spreading code for receiving the radio frame at the period of the next radio frame to the phase corresponding to the radio frame of the next period to try the despread of the radio frame signal in the upstream traffic channel. Further, sequentially advancing the phase of the spreading code for every period of said radio frame until synchronization is established.
Bringing the phase of the spreading code for receiving the radio frame in the upstream traffic channel at the second base station into coincidence with the phase of the spreading code of the radio frame in the upstream traffic channel from the mobile station to perform the phase correction.
Bringing the phase of the spreading code for receiving the radio frame in the upstream traffic channel at the second base station into coincidence with the phase of the spreading code of the radio frame in the upstream traffic channel from the mobile station to perform the phase correction.
The handover method according to the present invention further includes the second base station, temporarily setting the spreading code of the phase corresponding to the frame number advanced by a predetermined number from the frame number of the radio frame in the traffic channel in communication which is sent from the first base station.
Despreading by the temporarily set spreading code for each radio frame signal of the upstream traffic channel sequentially transmitted from the mobile station until the establishment of synchronization is detected.
The handover method according to the present invention further includes the second base station, detecting the frame number of the perch channel of the second base station when notified of time difference information of frame timing within the one frame from the first base station. Further, transmitting a first transmission delay measurement-use signal to the first base station.
The first base station transmitting to the second base station a second transmission delay measurement-use signal including the frame number of the traffic channel at the first base station when receiving the first transmission delay measurement-use signal.
The second base station finding an amount of transmission delay between the first base station and the second base station by using a difference between a value of the frame number, at the reception of the second transmission delay measurement-use signal, of the perch channel of the second base station and a value of the frame number, at the transmission of the first transmission delay measurement-use signal, of the perch channel of the second base station.
The second base station, correcting the frame number of the traffic channel of the first base station included in the second transmission delay measurement-use signal based on the amount of transmission delay, to make the spreading code of the phase corresponding to the corrected frame number as the spreading code for receiving the radio frame in the upstream traffic channel of the second base station.
Bringing the phase of the spreading code for receiving the radio frame in the upstream traffic channel of the second base station into coincidence with the phase of the spreading code of the radio frame in the upstream traffic channel from the mobile station to perform the phase correction.
The handover method in a CDMA mobile communication for transmitting and receiving between a mobile station and a base station an upstream traffic channel signal and a downstream traffic channel signal in units of a radio frame having a predetermined length. The upstream traffic channel signal from the mobile station to the base station is spread by a spreading code having a plurality of periods of the frames as one period and transmitting the spread signal.
The method including a second base station which is the destination of the handover after performing the phase correction, starting the transmission of the downstream traffic channel signal.
The handover method according to the present invention further includes that the second base station notifies the start of the transmission of the downstream traffic channel signal via the first base station to the mobile station. Further, the mobile station switches a communication frequency band from the frequency band of the first base station to the frequency band of the second base station when receiving the notification.
Further, the handover method according to the present invention includes that the mobile station sends the time difference information of the frame timing within said one frame to the first base station and then monitors the transmission start of the downstream traffic channel signal from the second base station.
The communication frequency band is also switched from the frequency band of the first base station to the frequency band of the second base station when detecting the transmission start of the downstream traffic channel signal from the second base station.
Further, the present invention provides a handover method in CDMA mobile communication for transmitting and receiving between a mobile station and a base station in an upstream traffic channel signal and a downstream traffic channel signal. The communication is performed in units of a radio frame having a predetermined length, for spreading the upstream traffic channel signal from the mobile station to the base station by a spreading code having a plurality of periods of the radio frame as one period and transmitting the spread signal.
The method includes the mobile station, after sending the time difference information of the frame timing within one frame to a first base station in communication, continuing the communication with the first base station for a predetermined time period.
The second base station which is the destination of handover, performs the phase correction when the upstream traffic channel signal is not received from the mobile station, notifying to the mobile station of an alarm via the first base station within the predetermined time period.
The mobile station switching the communication frequency band from the frequency band of the first base station to the frequency band of the second base station after an elapse of the predetermined time period if there is no alarm.
The present invention also provides a handover method including a mobile station that switches the communication frequency band from the frequency band of the first base station to the frequency band of the second base station immediately after sending time difference information of the frame timing within one frame to the first base station in communication. Further, the second base station performs phase corrections.
The present invention provides a mobile station that measures the time difference of frame timings within one frame between the radio frame in the traffic channel with the first base station and the radio frame in the perch channel from the second base station. Then sending the time difference information of frame timing within the one frame to the base station.
Further, the first base station, sending the time difference information of the frame timing within one frame sent from the mobile station via the higher rank communication network to the second base station. The second base station corrects reception timing for bringing the frame timing of the radio frame in the upstream traffic channel of the second base station into coincidence with the frame timing of the radio frame in the upstream traffic channel from the mobile station. This is accomplished by using the time difference information of the frame timing within the frame sent from the first base station.
The mobile station initializes the phase of the spreading code in the upstream traffic channel when switching the communication frequency band from the frequency band of the first base station to the frequency of the second base station alternatively sending the time difference information of the frame timing within the one frame to the first base station.
The second base station also initializes the phase of the spreading code for receiving the radio frame in the upstream traffic channel when the time difference information of the frame timing within the one frame is sent from the first base station.
Further in the handover method, the second base station performs the phase correction as set when the establishment of synchronization is not detected when receiving the upstream traffic channel signal from the mobile station.
A base station in a CDMA mobile communication system according to the present invention for transmitting and receiving with a mobile station in an upstream traffic channel signal and a downstream traffic channel signal. The communication is performed in units of a radio frame having a predetermined length, for despreading the upstream traffic channel signal from the mobile station to the base station by a spreading code having a plurality of periods of the radio frame as one period and receiving the despread signal.
The base station includes means for receiving time difference information of frame timings within one frame between a radio frame in a traffic channel and a radio frame in a perch channel of a base station of the destination of handover sent from the mobile station in communication.
Means for sending a frame number of the radio frame in the traffic channel of the mobile station and the time difference information of the frame timing within one frame sent from the mobile station to the base station of the destination of handover via higher rank communication network.
Means for performing the phase correction for bringing a phase of a spreading code for receiving the radio frame in the upstream traffic channel of the mobile station into coincidence with a phase of a spreading code of the radio frame in the upstream traffic channel from the mobile station. This is accomplished based on the time difference information of the frame timing within the one frame and the frame number of the radio frame in the traffic channel which are both sent from the base station in communication.
The base station according to the present invention is also provided with means for sequentially incrementing every other frame number of the radio frame notified from the base station in communication for every period of the radio frame until synchronization is established. Further, means for despreading the upstream traffic channel signal by a spreading code of a phase corresponding to the frame number to detect the establishment of synchronization to perform the phase correction.
According to the present invention, the base station is also provided with means for temporarily setting a spreading code of a phase corresponding to the frame number advanced by a predetermined number from the frame number of the radio frame notified from the base station in communication. Further, means for despreading by temporarily setting the spreading code for each radio frame signal in the upstream traffic channel sequentially transmitted from the mobile station until the establishment of synchronization is detected to perform the phase correction.
The base station according to the present invention also includes means for detecting the frame number in the perch channel when notified of time difference information of the frame timing within the one frame from the base station in communication with the mobile station. Further, means for transmitting a first transmission delay measurement-use signal to the base station in communication with the mobile station.
Means for transmitting to a base station of the destination of handover a second transmission delay measurement-use signal including the frame number in the traffic channel when receiving the first transmission delay measurement-use signal from the base station of the destination of handover.
Means for receiving the second transmission delay measurement-use signal and finding an amount of transmission delay between the base station in communication with the mobile station and the base station which is the destination of handover. The amount of transmission delay is found from the difference between the value of the frame number in the perch channel at the time of reception of the second transmission delay measurement-use signal and the value of the frame number in the perch channel at the time of transmission of the first transmission delay measurement-use signal.
Means for correcting the frame number in the traffic channel included in the second transmission delay measurement-use signal based on the amount of transmission delay, to make the spreading code of the phase corresponding to the corrected frame number as the spreading code for receiving the radio frame in the upstream traffic channel after handover.
The base station is provided with means for starting the transmission of the downstream traffic channel signal after handover after performing the phase correction.
The base station is also provided with means for notifying the start of transmission of the downstream traffic channel signal via the base station in communication with the mobile station to the mobile station.
Further, the base station is provided with means for notifying the mobile station of an alarm via the base station in communication with the mobile station when the upstream traffic channel signal is not received from the mobile station within a predetermined time period after performing the phase correction.
The base station according to the present invention includes means for receiving time difference information of the frame timings within one frame between a radio frame in a traffic channel and a radio frame in a perch channel of a base station, which is the destination of the handover sent from the mobile station.
Means for sending the time difference information of the frame timing within the one frame sent from the mobile station via the higher rank communication network to the base station which is the destination of handover.
A reception frame timing correcting means for bringing the frame timing into coincidence with the frame timing of the radio frame in the upstream traffic channel of the mobile station. This is accomplished by using the time difference information of the frame timing within one frame sent via the higher rank communication network.
Means for initializing a phase of a spreading code that receives the upstream traffic channel signal when receiving the time difference information of the frame timing within one frame via the higher rank communication network.
The base station according to the present invention also is provided with means for performing the phase correction with respect to the upstream traffic channel signal after handover.
Further, according to the present invention, a mobile station in a CDMA mobile communication system for transmitting and receiving with a base station in an upstream traffic channel signal and a downstream traffic channel signal in units of a radio frame having a predetermined length. Further, for spreading the upstream traffic channel signal of the base station by a spreading code having a plurality of periods of the radio frame as one period and transmitting the spread signal.
The mobile station including means for measuring the time difference of the frame timing within one frame between a radio frame in a traffic channel with a first base station in communication and a radio frame in a perch channel from a second base station, which is the destination of handover. Further, means for sending the radio frame phase information indicating only the time difference of the frame timing within the one frame to the first base station.
The mobile station is also provided with means for switching the communication frequency band from the frequency band of the first base station to the frequency band of the second base station when receiving the notification of start of the transmission of the downstream traffic channel signal from the second base station via the first base station.
The mobile station according to the present invention also includes means for monitoring the transmission start of the downstream traffic channel signal from the second base station after sending the radio frame phase information to the first base station means for switching the communication frequency band from the frequency band of the first base station to the frequency band of the second base station when detecting the transmission start of the downstream traffic channel signal from the second base station by the means for monitoring the transmission start.
The mobile station according to the present invention also includes means for continuing the communication with the first base station for a predetermined time period after sending the radio frame phase information to the first base station. Means for receiving an alarm notified from the second base station via the first base station.
Means for switching the communication frequency band from the frequency band of the first base station to the frequency band of the second base station after an elapse of the predetermined time period when the alarm is not received within the constant time. The mobile station is also provided with means for switching the communication frequency band from the frequency band of the first base station to the frequency band of the second base station immediately after sending the radio frame phase information to the first base station.
The mobile station is also provided with means for initializing the phase of the spreading code in the upstream traffic channel after sending the radio frame phase information to the first base station.
The mobile station is also provided with means for transmitting the upstream traffic channel signal to the second base station with the same transmission power, when communicating with the first base station as an initial transmission power after handover.
The mobile station is also provided with means for transmitting the upstream traffic channel signal to the second base station with the transmission power designated by the second base station via the first base station as an initial transmission power after handover.
The mobile station also provided with means for determining an initial transmission power after handover based on the received power of the perch channel from the second base station.
Further, the mobile station is provided with means for determining an initial transmission power after handover based on the received power of the downstream traffic channel from the second base station.